1. Field of the Invention
The present invention relates to the mining engineering and, more specifically, to a power unit for destruction of rocks.
The present invention may be used for breaking off large rock monoliths along the line of blastholes followed by disintegration of monoliths into blocks, for explosion-free driving of rock workings, for destruction of foundations of old buidlings and other strong footings. When the power unit is used in boreholes, it may be employed for weakening a difficult-to-collapse roof in mining of the stratified deposits, for positive degassing of coal seams, for fracturing of oil reservoirs and gas-bearing strata, for studying the stressed and deformed state of a rock mass under natural conditions.
The present invention may be used in the metal-working industry as a powerful small-size drive for actuating means of presses, jacks, guillotines and other installations utilizing considerable directed forces.
2. Description of the Prior Art
Known in the prior art is a power unit (cf. USSR Inventor's Certificate No. 420,779, cl. E 21c 39/00, 1974), comprising a housing internally accommodating along the longitudinal axis and throughout the entire length thereof a tubular elastic vessel with sealing means disposed at the ends thereof. The housing of the given power unit comprises two portions one of which is stationary relative to the axis of the power unit, while the other one is an extendable metal plunger. When pressure in the hydraulic system is raised the inner space of the elastic vessel is filled with a working meduim and the vessel is expanded. As the volume occupied by the elastic vessel is restricted by the housing portions, the plunger extends and acts upon an object.
The power unit develops the force in a present direction proportionally to the area of the plunger surface in contact with the elastic vessel. Thus the efficiency of the power unit of the above-mentioned design is low.
We understand the efficiency as a ratio between the force developed by the power unit in a preset direction and the force developed by the elastic vessel. The transverse component of the working medium pressure built up by the elastic vessel, the vector of which is perpendicular to the vector of the force developed by the power unit in the preset direction is not utilized for developing the force in the preset direction. The transverse component causes deformation of the stationary portion of the housing bringing about therein plastic strains which reduce the reliable operation of the power unit. When pressure of the working medium in the elastic vessel is raised, it increases the value of the transverse component. Increase of the transverse component causes formation of clearances between the plunger and the stationary portion of the housing in which the material of the elastic vessel "flows". This condition leads to rupture, i.e. to depressurization of the elastic vessel. The ways for improving rigidity of the housing lead either to an increase in the metal content or to a substantial complication of the power unit manufacturing methods on the whole.
Attempts of increasing the efficiency of the power unit gave rise to the construction disclosed in USSR Inventor's Certificate No. 1,033,819, cl. E21C 37/06, 1982.
The known power unit comprises a longitudinally split housing internally coaxially accommodating a tubular elastic vessel and two expanding inserts, each of which is disposed on the side of the parting line of the housing. In the plane perpendicular to the housing axis the insert has a trapezoidal section the larger base of which bears against the elastic vessel and the sides bear against the inner wall of the housing. In addition, the power unit incorporates two holders each of which is provided with a pipe union intended for delivery of a working medium into the space of the elastic vessel. Each of the ends of the elastic vessel is disposed between the pipe union and the holder. A perforated tubular core is arranged in the space of the elastic vessel along the longitudinal axis thereof. Each end of the perforated tubular core is made in the form of a pipe union. Each of the holders is essentially a sleeve with the internal thread engaged with the external thread of the pipe union; thus the holders are rigidly connected with each other through the medium of the perforated core. The holders are intended for sealing the ends of the elastic vessel.
When the working medium is delivered under pressure into the inner space of the elastic vessel the housing portions are expanded both by the elastic vessel and the expanding inserts.
The known power unit failed to find wide application in breaking natural rock monoliths, for example, granite, off the rock mass because of a limited force developed by the elastic vessel, for example, about 10 MPa, as the power unit cannot develop the required force in the preset direction, i.e. in the direction perpendicular to the plane of the break. This is explained by that the substantial axial loads arising in the tubular core stretch it. This leads to formation of a clearance between the end of the housing and the end of each of the holders facing the elastic vessel. The material of the elastic vessel "flows" in this clearance and then the vessel ruptures. Besides, the core stretching weakens the sealing of the elastic vessel ends which brings about leaks of the working medium. The core stretching may be reduced at the cost of increasing the core cross-sectional area. However, it leads to a sharp increase in the overall dimensions and metal content of the power unit, or in case of maintaining the original overall dimensions of the power unit it brings about a decrease in the working travel of the housing movable portions and a rise of the unit pressure at the place where the side surface of the inserts come in contact with the inner surface of the housing which is not desirable, as it involves the use of special materials and lubricants.
It should also be noted that the trapezoidal shape of the expanding inserts is not optimum, as in case of a non-uniform bearing of the housing expandable portions against the surface of a blasthole or a borehole, a clearance is formed between the side surface of each insert and the inner surface of the housing in which the material of the elastic vessel will "flow".